Lightroom does not have an edit history like there is in Lightroom Classic. However, to undo the most recent edit it is possible to use Cmd+Z to undo that process. And continual use of the keystroke combination will undo additional previous changes. But that is the extent of the undo process available in Lightroom 4.1.
Lightroom is a non-destructive editor. That means that your edits do not change the image itself, but are stored in a kind of 'to do list'. And that means that you can undo any edit by simply moving the slider back to the original (or previous) position.